Programmable Logic Controllers

How to Configure 4-20 mA Analog Inputs on a PLC

by Johan Esvelt from DIVIZE

A PLC (Programmable Logic Controller) is used for the control of industrial machines and process installations. The PLC was designed specially for this purpose and offers the possibility of a flexible configuration by means of hardware and software to be adapted to the machine or process which needs to be controlled. Analog signals such as pressure and temperature from the process are evaluated by the PLC and based on these signals the process is controlled by the PLC. Analog signals need to be connected to the PLC and configured. Because of the modular design and configuration of the PLC many things can go wrong. This article gives some guidelines.

Siemens S7 Indirect Addressing

by Automation Training

The following is provided by Automation Training from their excellent Siemens Step 7 training manual. This is a really nice explanation of a difficult but important subject. Check out their website for hands-on and online training classes.

Learn Ladder Logic with a Free Version of RSLogix 500 and RSEmulator 500

One of my most common questions is, “Where can I get a free download of RSLogix 500?”  For any serious development with SLC500 or MicroLogix there is no free option but there is a nice free option if you only want to learn and/or program a MicroLogix 1000 or 1100.  Programming a MicroLogix is very very similar to programming a SLC500 or in that case a PLC5 too. 

Allen Bradley offers as a free download a software package called RSLogix Micro Starter Lite which is essentially the same programming environment as RSLogix 500.  On top of that, they also offer RSLogix Emulate for free so that you don’t even need a PLC to run and test your ladder logic.  Keep reading and I’ll show you how to get the software and set it up.

RSLogix 5000 Add-On Instructions

by John Schop

One of the most powerful newer features of the RSLogix 5000 program is the ability to create Add-On Instructions. This allows a programmer to define an instruction that contains a commonly used function or algorithm (as a set of instructions), and use it as one instruction.

To illustrate how this works, I am going to create an instruction that operates a cylinder, and because I’m making an add-on instruction, I can use that same instruction to control any number of cylinders in my application

Connecting Excel to ControlLogix

by John Schop

Have you ever lost data in a CLX processor, because you downloaded new code? Unfortunately, when you donwload a program to a ControlLogix processor, you also download the values of the tags (variables).

A solution to this problem that could be useful, is an Excel sheet that reads and writes values to the ControlLogix processor using the DDE/OPC capabilities of RSLinx.

In this article, I will show you how to create one of these sheets for your projects.

Here's what you'll need:

User Defined Data Types (UDTs) and OOP

by John Schop

For years now, Object Oriented Programming paradigm (or OOP) has been a commonly used programming practice, and has of course found its way into industrial automation as well.

An Introduction to Grafcets

by John Schop

I often find that using SFC's or Grafcets is the easiest way to design industrial automation systems. I have worked for several machine builders, and one of them had given the term 'SFC logic' another meaning. There was absolutely no process in their PLC logic that was not documented by an SFC or as I like to call it, a Grafcet. After some getting used to that, I absolutely loved the way it enabled me to program and troubleshoot complex machinery, and ever since, I've tried to use this method whenever I could.

Sequential Function Charts for All

Implementing Sequential Function Chart Designs using Ladder Diagram Programming Language for Programmable Logic Controllers

by James McWhinnie
Napier University, Edinburgh, Scotland.


Sequential Function Charts (SFC’s) have long been established as a means of designing and implementing sequential control systems utilising programmable controllers. The Programming Standard IEC 61131-3 includes a graphical implementation of SFC’s in its suite of programming languages.

Connecting IFIX SCADA to Siemens S7 using TCP/IP

Setting up an S7 connection using TCP/IP

The TCP/IP method of communication to the S7-300 and S7-400 PLC's via TCP/IP communication module uses the S7WIN, S7WINSP, S7NT, or S7NTSP protocol.

The Logix5000 Essential Manuals

The Allen Bradley Logix5000 family (ControlLogix, CompactLogix, FlexLogix, SoftLogix) has some very good manuals. If you are just starting out or need a refresher here are the key manuals and the order I would read them. If you have RSLogix 50000 installed then you will find some of these in the Help > Online Books menu. Revision 16 also has some great videos in the Learning Center.